Good job on the seam ripper. Love the color.
I've made a bunch of both brands (PSI & Berea) seam rippers and I'm back to being more of a PSI fan.
The original PSI kits (like the one you got from Rockler) had a spring that was a little over half the length of the one in the current kits. There was nothing to seat the springs and the would push down in the tube sometimes and would not hold the ripper. The longer springs seem to push against each other if you make the double like you did. This keeps them in place and working.
One other thing on the PSI kits, they offer a stiletto replacement point and needle threader kits. I've started making these in pairs. One would have a seam ripper on one end and a stiletto on the other. The second would have a seam ripper and a needle threader. That way you will usually sell two instead of one.
On the Berea kit, the O-rings provide positive hold, but if the user regularly takes it out and puts it back into the handle, the O-rings will wear and fall off. I stocked up on replacement O-rings and usually give a small plastic bag with 4 rings to every customer. The O-rings are a pain to get on too.
One thing I learned from my wife the quilter is that if your customers are older, make them wider. Older hands can't grip a pen blank comfortably for very long. The other lesson I learned is to leave one side flat. If you make it round, it rolls off the table or sewing machine. Good luck with them. They are fun to make.
Steve